Mark Bailey: Rethinking citrus in Florida

For many years, citrus has been plagued with/by an onslaught of plant diseases from citrus canker to citrus greening. Especially after the arrival of citrus greening, citrus generally has not been recommended as a fruit tree for residential growers. While citrus diseases remain a significant risk, citrus still has a place in the yard and in the field. It is the combination of the right kind of citrus planted in suitable conditions that can allow some citrus to thrive. 

First, it is extremely important to understand where citrus originated and the conditions that it naturally adapted to. When these are understood, it becomes a lot easier to successfully grow citrus. All oranges, lemons, limes, tangerines, mandarins and grapefruit belong to the genus Citrus; however, most of these are, in fact, hybrids that likely originated from three different species. The three species — Citrus medica, Citrus reticulata and Citrus maxima — all originate from the geographic region of southeast Asia. Specifically, they originated as a jungle understory tree in that region. In those conditions, there is very limited sunlight due to the thick tree canopy blocking most of the light. Given that citrus trees are not known to grow to enormous heights, they tend to remain underneath the canopy and are naturally adapted to partly shaded conditions. As such, they are less stressed in partial shade compared to citrus that is grown in full sun throughout the day. When citrus trees are grown in full sun, they are more stressed and, as a consequence, they are more likely to be affected by severe disease symptoms, such as from citrus greening disease. A logical question might be asked: “Why are thousands of acres of citrus grown in full sun if they are more stressed?” The simple answer to that question is that it’s the way that virtually all agricultural crops are grown, and that’s the way past generations grew the crop. Another answer is that citrus may be slightly more productive in full sun, but at the great cost of severe diseases weakening or killing the trees. Citrus production methods need to change if growers — at any scale — want to grow citrus sustainably. 

Going back to the three different species from which the hybrids originated, they tend to be much less susceptible to major diseases like citrus canker and citrus greening. The problem is that two out of the three produce very low-quality fruit. The one species that really shines is Citrus reticulata, the mandarin orange. Most commercial varieties of mandarin oranges have some slight contributions of genetics from pomelos (Citrus maxima); however, they are very closely related to the wild mandarins. Mandarins, and many closely related hybrids, are known to be tolerant to both citrus canker and citrus greening. Mandarin orange hybrids that have demonstrated tolerance to citrus greening include Bingo, Tango, Sugar Belle and Sundragon. Mandarins also have the desirable characteristic of being far more cold-tolerant than most other kinds of citrus. 

For those who want to grow citrus in a way that is closest to their natural adaptations, begin by selecting a location that has partial shade throughout the day. If no shade is available, there is the option of using shade cloth, ranging from 30% to 50% shade, that is placed over the tree. Next, ideally, choose a mandarin orange or related hybrid and keep the tree irrigated as needed, allowing it to become established. Once the trees become fully established, they should not require repeated applications of pesticides for them to thrive. Several applications of citrus fertilizer, typically in spring and late summer, can encourage new growth. Trees grown in these conditions may take several years before they begin to yield substantial quantities of fruit. 

Citrus has become naturalized throughout Florida, and when they grow in suitable conditions, they tend to thrive. There are many instances where wild citrus have been loaded with citrus fruit and yet it has never been sprayed with pesticide or even been provided with fertilizer. The trees simply grew in the conditions they were naturally adapted to. 

So, the next time there is a visit to a local nursery, keep an eye out for citrus trees. They still have a place in the yard.